feat(localdb): one-time alarm-historian.db migrator

Copies the pre-consolidation store-and-forward queue into the consolidated
database on first boot, then renames the legacy file aside. Rows are in that
file precisely because the historian could not be reached, so dropping them
on upgrade would discard exactly the alarm audit trail the queue exists to
protect.

Runs last in OnReady, after every RegisterReplicated call. It is the only
thing in OnReady that writes rows, and capture is trigger-based: a migration
that ran before registration would recover the backlog locally and never
replicate a line of it, silently and permanently.

Ids are derived from the payload rather than the plan's mig-{node}-{legacyId}
scheme. Node-prefixing solves the collision the legacy AUTOINCREMENT key
would cause -- node A's row 7 and node B's row 7 are different alarms -- but
it preserves a duplication that should be collapsed instead. A warm pair's
two legacy files OVERLAP: HistorianAdapterActor default-writes while its
redundancy role is unknown, so both nodes accepted the same transitions
during every boot window. Prefixed ids would carry those duplicates into the
merged buffer forever; equal-payload ids converge them. The same property
makes a crash between commit and rename harmless under INSERT OR IGNORE.

OnReady now takes IConfiguration rather than offering an overload that skips
the migration. A wiring mistake that silently discarded a node's undelivered
alarm history is not a mistake worth making possible.

The copy is restricted to the columns the legacy table actually has. Naming
a column an older build never wrote throws "no such column", which would
discard every row in the table rather than the one field.

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

docs/plans/2026-07-20-localdb-adoption-phase2.md.tasks.json

@@ -37,10 +37,11 @@
     {
       "id": 4,
       "subject": "Task 4: One-time alarm-historian.db legacy migrator",
-      "status": "pending",
+      "status": "completed",
       "blockedBy": [
         3
-      ]
+      ],
+      "note": "AlarmSfLegacyMigrator runs LAST in OnReady (which now takes IConfiguration - no skip-migration overload exists). DEVIATION D-6: ids are the payload hash (AlarmSfSchema.DeriveId, lifted out of the sink) rather than mig-{node}-{legacyId} - a warm pair's two legacy files OVERLAP, and node-prefixing would carry that duplication forward forever. DEVIATION: tests live in Host.IntegrationTests; the plan's Host.Tests project does not exist."
     },
     {
       "id": 5,